The present invention relates to a semiconductor power module for use in power electronics. More particularly, the present invention relates to a semiconductor power module having a multilayer or sandwich design.
The reliability, lifetime and density of semiconductor power modules can be increased if new material combinations are employed, or if new methods are applied with which the individual components can be combined into a single unit for integration into various types of circuits. An increased density of power semiconductor components requires a design which adequately isolates the power semiconductor elements and which exhibits excellent heat conductivity for dissipating heat that is generated at the p-n junctions.
In the case of an isolating design of power semiconductor modules having copper-coated insulating and heat-conducting substrates, the active components are affixed through soldering. Such positive connections ensure excellent heat dissipation and well-adjusted positioning of the individual elements within the arrangement.
Until now, in commutation circuits with circuit arrangements for conversion and driving technology, the establishment of switched connections of semiconductor elements on the surface of a circuit has conventionally been accomplished by means of bonding methods, since the relatively fine structure of the chip contact surfaces does not allow any other contacting methods. For example, connections between chip contact points and the secondary joining elements on DCB ceramics often use aluminum wires of up to 330 .mu.m in thickness. The aluminum wires are bonded in multiple parallel fashion through positive subject jointing, such as, for example, by a method employing ultrasound. During bonding, ultrasound and the pressure of a bond chisel produce a structural change in the aluminum wire, which is detrimental to stability in long-term operation. The aluminum wire eventually develops structural cracks at the bonding points, which lead to the breaking of the connection between the chip contact surface and the aluminum wire. Consequently, it is not yet possible to achieve the desired maximal long-term stability with this technology.
As is disclosed in DE 36 37 513 A1, a two-layer metal coating can be used to reduce the large number of connections in the front of the power components (such as MOSFETs (Metal Oxide-Silicon Field Effect Transistors) or IGBTs (Isolated Gate Bipolar junction Transistors)), which are repeated and must be isolated from each other, to a smaller number that can be soldered or pressure-contacted. However, it is generally still considered state of the art in power electronics to achieve the required isolation stability between live parts by means of additional protection, such as silicon rubber in the form of an isolating cast or soft cast.
On the other hand, DE 31 19 239 A1 discloses a multilayer structure of large-scale integration (LSI) semiconductor components. In this case, due to very low voltages and voltage differences between the individual internal interconnections, it is not necessary to isolate the individual contact lines or electrical connections from each other.
Another method is disclosed in DE 44 07 810 A1. In power structures of that type, the necessary isolating cast serves simultaneously as a pressure element. Therefore, even though its size is reduced in comparison with devices made according to prior art, the design of this circuit arrangement still has a certain minimal height. In DE 41 32 947 A1, positive substance jointing (soldering) is replaced by positive substance pressure contacting (adhesive or glue paste fixation), whereby individual components are contacted on one or both sides by flexible circuit boards. However, this approach does not satisfactorily address the problem of achieving the required flash-over resistance when the voltage differences inside the circuit are high.